1. Field of the Invention
The present invention relates to a heating structure and its temperature control method, and more particularly to performing heating with a PTC element, by the feature of the PTC element for direct current square wave signals respectively converted by an AC phase shaping circuit and an AC phase delay shaping circuit to generate phase shifting to immediately control turning on/off of a trigger circuit, thereby the PTC element is heated or reduced in temperature and therefore a heat generating line can keep at a predetermined working temperature. The present invention is applicable to heat generating devices such as electric ovens, and heating blankets etc.
2. Description of the Prior Art
Heating structures have been widely used in the markets now; such as shown in FIG. 7 which depicts a quite normal heating pad structure, it is provided mainly on a bag with a set of electric conductive plates a1 stacking one on the other, the two electric conductive plates a1 are sandwiched therebetween a plurality of ceramic electric resistances a2, and a soft heat durable insulating member a3 envelops the two electric conductive plates a1 to form the heating pad “a”. The ceramic electric resistances a2 is a positive temperature coefficient (PTC) element; when the two electric conductive plates a1 are electrically turned on, the resistance of the PTC element will have a hasty change in pursuance of rising of temperature; when the value of the resistance is increased to render the electric current unable to be conducted, a circuit breaking is formed, and a fixed temperature can be obtained under control.
And as shown in FIG. 8 which shows a structure disclosed in a U.S. Pat. No. 5,081,341 to directly make short circuit of a heat-generating electric resistant line b1 in a fabric “b” and to make two contact portions b2 protrude outwards, and also to control conduction of electric current by switching a switch b3 for heating. This technique does not disclose timely measuring as the former conventional technique does, and is unable to make multistage temperature control.
Therefore, the heating mode using a PTC element as a measuring structure in cooperation with a heat generating line to adjust and control temperature is widely used. As shown in FIG. 9 which shows a U.S. Pat. No. 5,861,610, a core member “c” is wound and enveloped thereover with a heating conductive line c1, a second insulating layer c2, a measuring line c3 and a first insulating layer c4 sequentially, the measuring line c3 is made of PTC material (nickel alloy). When the temperature of the measuring line c3 is raised following rising of the temperature of the heating conductive line c1, or the resistance of the measuring line c3 is changed by a high temperature, a comparing circuit in a controller compares and adjusts the amount of current input to the heating conductive line c1 with the result of comparing to control the heat-generating temperature to be within the range set by a user.
The abovementioned techniques were also disclosed in a U.S. Pat. No. 6,300,597, a U.S. Pat. No. 6,310,322 and a U.S. Pat. No. 6,768,086. Moreover, as shown in FIG. 10 which shows a circuit control diagram of a U.S. Pat. No. 6,222,162, the patent disclosed another example of application of a PTC element, the big difference of which from the above conventional structures is that, it uses a single PTC alloy; it controls turning on or breaking of a circuit by measuring its resistance and voltage changed after heating, thus an objective of heating with a constant temperature can be achieved.
We can see from the above granted patent cases that, direct generating heat with a heat-generating electric resistant line or using a PTC element on a temperature controlling and measuring technique is quite known and used presently, however, the above various modes have rooms for improvement:                1. Most of the conventional techniques shall each have simultaneously two loops including a heating and a measuring loop provided in a heating pad or a heat generating structure, and shall each have four contacting portions extended outwards (to respectively connect with two loops), and shall respectively connect with a heating and a comparing circuit, allocation of their electronic elements appears complicate, this will increase the cost of production and the rate of fault.        2. No matter two functions of heating and measuring are simultaneously obtained by using a single PTC alloy, or the two functions are obtained by using two different loops, when a temperature controlling device of a heat generating structure is damaged, its heating conductor will continue to heat, thereby a danger of conflagration can be induced. The above conventional techniques did not provide a guarantee of safety by making good uses of the features of the PTC elements.        
In view of this, and in order to get rid of the above defects to render a heat generating structure and its temperature control method not only able to control temperature by the feature of the PTC element to simplify the composition of the element and save the cost of material as well as lower the rate of fault, but also able to automatically turn off in case of overcurrent to obtain an effect of safety and protection, the inventor developed the present invention based on his experience of years and nonstop study as well as improvement.